A man pulls out a bag of marijuana to fill a pipe, Aug. 16, 2013, in Seattle. / Elaine Thompson, AP

by Gary Strauss, USA TODAY

by Gary Strauss, USA TODAY

Bolstered by decriminalization laws in Washington state and Colorado, marijuana could become an $8.2 billion retail business by 2018, an industry trade journal says.

That's a 33% jump over earlier forecasts and a five-fold increase over expected 2014 retail and medical sales, according to Marijuana Business Daily.

The publication boosted 2018 sales estimates due largely to a Justice Department decision to take a hands-off approach to drug enforcement in Colorado and Washington, which allow limited, legal use of pot, and the assumption that up to six more states could allow recreational and medical use.

Chris Walsh, editor of CannaBusiness Media, which publishes Marijuana Business Daily, said the $8.2 billion sales estimate could be conservative and doesn't include wholesale revenue or marijuana-related products. "The reality of retail sales could be larger,'' he said.

Recreational sales are predicted to hit up to $4.2 billion by 2018; medicinal sales up to $4 billion. The year would mark the first that recreational retail sale revenue would outpace medicinal sales, Marijuana Business Daily reports.

In Colorado, where retail sale of recreational pot began Jan. 1, state budget experts expect $1 billion in sales in 2015. Washington, where recreational sales begin June, could see $1.5 billion in annual sales by 2015.

Twenty states and the District of Columbia have legalized medical or recreational marijuana use. California, New York, Florida and New York are considering legalizing medicinal or recreational use. Alaska voters will decide whether to legalize recreational use in August.

How does $8 billion in annual sales compare to other markets? It's similar to the annual U.S. market for pet medications and the global market for premium chocolate, according to market researchers Packaged Facts and Mintel.